The present invention relates to an actuator having a drive element which can be driven in reaction to electrical operation of a coil device, said drive element consisting of magnetic shape-memory material according to the preamble of the main claim.
Such devices are known from the prior art and utilise the effect that, under the influence of a magnetic field, so-called shape-memory materials (also frequently called shape-memory alloys, MSMA) perform an expansion movement which in the direction of expansion (=drive direction) is typically in the low single-figure percentage range relative to the length of the element.
In such devices, there is the principal requirement that the magnetic field effecting the expansion and/or the longitudinal alteration of the drive element has to be located perpendicular to the expansion and/or drive direction (working axis). Accordingly, for electromagnetic coil devices which generate the required magnetic field, this means that said coil devices (for example in a coil pair) have to be located with their axis of symmetry perpendicular to the working direction of the actuator. This results in large constructional spaces (which is frequently disadvantageous), in particular when two coils are provided symmetrically on both sides of the shape-memory element.
It is, therefore, known from the prior art to use drive elements consisting of a magnetic shape-memory material at different points along a magnetic circuit (namely in a gap formed between housing elements of a magnetically conductive housing) which, however, results in mechanically complex and/or geometrically and structurally complicated embodiments which also do not provide the mechanical drive energy in an optimal manner.
In particular, none of the known embodiments for acting on a magnetic shape-memory material to produce an actuator permits the use of commonly available sub-assemblies and components, as are known from conventional embodiments of electromagnetic actuators, namely elongate, axially extending armature tappets which are surrounded by a typically cylindrical coil (and for which the installation spaces are typically dimensioned, namely in a motor vehicle).